The present application claims priority under 35 U.S.C. 119 of German Patent Application No. 100 23 568.9 filed May 15, 2000.
The invention concerns a focusing drive for optical instruments, in particular microscopes. It has a pinion and toothed rack arrangement as well as guidance means for displacing a device component with respect to a stationary further component.
With adjustment mechanisms of this kind, the problem often exists that aging and wear phenomena occur as the toothed rack and pinion interact, and jerky adjustment operations can result. The toothed racks must be carefully centered and aligned on the component that is to be displaced. This results in time-consuming and cost-intensive assembly procedures. Combined with the aforementioned wear susceptibility of such systems, with frequent use it is therefore impossible to obtain smooth, zero-backlash guidance over a long period of time.
It is therefore the object of the present invention to eliminate the disadvantages of known focusing drive solutions and to describe a smooth and zero-backlash guidance mechanism that moreover can be installed in the optical device without alignment elements, resulting in economical manufacture.
This object is achieved, according to the present invention, by a focusing drive of the kind cited initially in that it is fitted with a plastic toothed rack that is equipped with a plurality of support elements and comprises parallel-mounted slide rods as guidance means. Special support elements are arranged on the toothed rack on either side of its longitudinal extent. These can be cantilevered from the toothed rack in arm-like fashion. The support elements are advantageously located on the toothed rack in paired fashion, so that one left arm and one right arm form, so to speak an arm xe2x80x9cpair.xe2x80x9d It is also possible for the support elements to be cantilevered in L-shaped fashion on the toothed rack. In a particular embodiment of the present invention, the support elements are of resilient configuration. For example, they can have a stepped shape or be slightly S-shaped in longitudinal section. The support elements rest with their respective end regions against the device module that is to be displaced. A one-piece configuration of the toothed rack is advantageous.
The focusing drive according to the present invention furthermore has parallel slide rods as guidance means for the displacement of a device module relative to a stationary device stand. These rods can be positioned loosely in V-grooves, the grooves being provided on the one hand in the device module to be displaced and on the other hand in the stationary device stand. According to the present invention, the slide rods are held under compressive stress in their respective positions. This is implemented by the fact that the device stand externally surrounding the slide rods is physically equipped and dimensioned so as to result in a pressure-generating clamping effect on the slide rods. It is thereby possible to provide means for stable retention and controlled modification of the pressure. These means can comprise a rotary knob that is under a spring preload. Particularly significant is the fact that the slide rods are made of an electrically conductive plastic material, and are circular in cross section. Because of the specific material selected, it is possible to create a focusing drive in which displacement along the slide rods is accomplished in dry sliding fashion. It is also possible to provide means for adjusting or changing the drag of the focusing drive. According to the present invention, this focusing drive is intended for use in antistatic optical devices, in particular microscopes.